The majority of fastener driving tools in use today are pneumatically actuated tools. Pneumatic fastener driving tools have been developed to a high degree of sophistication and efficiency, but require a source of air under pressure and are literally tied thereto by hose means. Under some circumstances, particularly in the field, a source of air under pressure is not normally present and is expensive and sometimes difficult to provide.
Prior art workers have also developed a number of electro-mechanical fastener driving tools, usually incorporating one or more flywheels with one or more electric motors therefor. Such tools require a source of electrical current normally present at the job site. As a result, this type of tool is also quite literally "tied" to a power source.
Under certain circumstances, it is desirable to utilize a completely self-contained fastener driving tool, not requiring a source of air under pressure or a source of electrical current. To this end, prior art workers have devised self-contained fastener driving tools powered by internal combustion of a gaseous fuel-air mixture. It is to this type of tool that the present invention is directed.
Exemplary prior art internal combustion fastener driving tools are taught, for example, in U.S. Pat. Nos. 2,898,893; 3,042,008; 3,213,607; 3,850,359; 4,075,850; 4,200,213; 4,218,888; 4,403,722; 4,415,110; and European Patent Application Nos. 0 056 989; and 0 056 990. While such tools function well, they are usually large, complex, heavy and awkward to use.
The fastener driving tool of the present invention comprises a self-contained internal combustion tool which is compact, easy to manipulate and simple in construction. The fastener driving tool is highly efficient, operating on a high compression ratio to convert most of the fuel energy into useful work. The tool utilizes a pair of coaxial upper and lower cylinders. The upper cylinder has a piston assembly and, during a tool cycle, serves as a compressor to replenish air under pressure in a combustion air chamber to which the upper cylinder is connected by a one-way valve. The lower cylinder is provided with a piston/driver which, during a tool cycle, drives a fastener into a workpiece and fills a return air chamber (to which the lower cylinder is connected) with air under pressure. The upper cylinder piston assembly and the lower cylinder piston/driver assembly, when in their normal positions, define a combustion chamber provided with an ignition means.
The fastener driving tool is provided with a positive, trigger-actuated cam system which sequences the tool through its cycle, upon actuation of the trigger. The cam system operates a series of two-way valves and an ignition device.